The present invention relates to a pigment-containing coloring material stably dispersible in high concentration in various organic solvents, and a process for producing the same.
This coloring material, as with conventional dyes or pigments, is used, either solely or after addition of an inverter component, as various coating systems, coating materials, printing inks, ink jet printing inks, toners, or compositions. In particular, color filters produced from the coloring material according to the present invention can have improved spectral characteristics (higher color purity, higher transmittance, and higher contrast) than conventional color filters.
Thus, the present invention relates to a color filter possessing excellent spectral characteristics (higher color purity, higher transmittance, and higher contrast) comprising a colored layer containing a pigment stably dispersible in high concentration in various organic solvents, particularly to a color filter for use in color liquid crystal displays.
In general, dyes have unsatisfactory resistance to light, heat, solvents, and chemicals. On the other hand, pigments involve problems of a lack of dispersion, dispersion stability, transparency, profile sharpness of absorption spectra or transmission spectra, or diffusion. In this respect, Japanese Patent Laid-Open No. 188234/1995 or Japanese Patent Laid-Open No. 6242/1996 proposes a novel coloring material having both an advantage of dyes and an advantage of pigments (good solubility of dyes and good weathering resistance of pigments) through the use of a soluble pigment precursor which can be converted to insoluble pigment particles having a size of nanometers by a chemical, thermal, or photolytic method or by laser or other beam irradiation.
The use of a coloring material disclosed in Japanese Patent Laid-Open No. 188234/1995 or Japanese Patent Laid-Open No. 6242/1996 permits the pigment to be evenly dispersed in high concentration in a polymer layer, but on the other hand, there is a disadvantage that elimination partially occurs due to volatilization of the precursor upon conversion of the soluble pigment precursor in the polymer layer to insoluble pigment particles by chemical, thermal, photolytic, or radiation induced means, leading to an uneven reduction in layer thickness. In the case of the soluble pigment precursor, in general, a bulky functional group is introduced to render the precursor soluble in a solvent, and the elimination of the bulky functional group converts the precursor to an insoluble pigment. This renders the above unfavorable tendency significant. Further, when the eliminated functionality is present in a large amount in the layer, there is a fear of the influence of the functionality. For these reasons, it is difficult to apply the coloring material to the field of applications where dimensional accuracy, particularly good coating smoothness are required, such as color filters.
When the soluble pigment is converted to the insoluble pigment in a solvent before coating formation from the viewpoint of avoiding this problem, the precipitation of the pigment extremely lowers the solubility of the pigment in the solvent, leading to the production of coagulation sediment. Therefore, the storage stability is poor, and the preparation of a highly concentrated solution per se becomes difficult.
Meanwhile, in the case of liquid crystal displays, a liquid crystal material is sealed into a gap of about 1 to 10 xcexcm between glass or other transparent substrates provided with transparent electrodes, and the liquid crystal is aligned in a given direction by a voltage applied across the electrodes to form transparent portions and opaque portions, thereby displaying an image. For color liquid crystal displays, a color filter for three primary colors of light is provided on any one of the transparent electrode substrates, and the three primary colors are added by shutter operation of the liquid crystal to display desired colors.
The color filter used in the color liquid crystal display comprises a transparent substrate, a colored layer, a protective layer, and a transparent conductive layer stacked in that order. The color filter and electrodes or transparent electrodes provided with a thin film transistor, which face colored pixels of three primary colors of RGB, are held while leaving a gap of several xcexcm therebetween, and a liquid crystal material is sealed into between the gap to form a liquid crystal display.
The colored pixels provided in the color filter are generally formed of a specific colorant, such as a dye or a pigment, in combination with a suitable resin, a binder, a polymer and/or an additive. Dyes generally have unsatisfactory resistance to light, heat, solvents, and chemicals. On the other hand, pigments involve problems of a lack of dispersion, dispersion stability, transparency, profile sharpness of absorption spectra or transmission spectra, or diffusion. In this respect, Japanese Patent Laid-Open No. 188234/1995 or Japanese Patent Laid-Open No. 6242/1996 proposes a coloring material having both an advantage of dyes and an advantage of pigments (good solubility of dyes and good weathering resistance of pigments) through the use of a soluble pigment precursor which can be converted to insoluble pigment particles having a size of nanometers by chemical, thermal, or photolytic means or by laser or other beam irradiation.
The use of a coloring material disclosed in Japanese Patent Laid-Open No. 188234/1995 or Japanese Patent Laid-Open No. 6242/1996 permits the pigment to be evenly dispersed in high concentration in a polymer layer of the colored layer constituting the color filter, but on the other hand, there is a disadvantage that elimination partially occurs due to volatilization of the precursor upon conversion of the soluble pigment precursor in the polymer layer to insoluble pigment particles by chemical, thermal, photolytic, or radiation induced means, leading to an uneven reduction in layer thickness. In the case of the soluble pigment precursor, in general, a bulky functional group is introduced to render the precursor soluble in a solvent, and the elimination of the bulky functional group converts the precursor to an insoluble pigment. This renders the above unfavorable tendency significant. Further, when the eliminated functionality is present in a large amount in the layer, there is a fear of the influence of the functionality. For these reasons, it is difficult to apply the coloring material to the field of applications where dimensional accuracy, particularly good coating smoothness are required, such as color filters.
When the soluble pigment is converted to the insoluble pigment in a solvent before coating formation from the viewpoint of avoiding this problem, the precipitation of the pigment extremely lowers the solubility of the pigment in the solvent, leading to the production of coagulation sediment. Therefore, the storage stability is poor, and the preparation of a highly concentrated solution per se becomes difficult.
The first invention has been made under these circumstances, and can overcome the above problems, although the reason why the above problems can be solved has not been fully elucidated. Specifically, according to the first invention, there are provided a coloring material comprising an insolubilized pigment dispersed stably in a solvent, said coloring material being produced by, in dissolving (1) a soluble pigment precursor, which is convertible into an insoluble pigment, in (2) a solvent capable of dissolving the soluble pigment precursor therein, allowing (3) a stabilizing agent, comprising an organic compound having a structure or a functional group capable of stabilizing the dispersibility of the insolubilized pigment in the solvent, to further exist, and, in this system, converting said soluble pigment precursor into an insoluble pigment, and a process for producing the same. The first invention further includes a coloring material wherein the above coloring material has been concentrated to obtain a solidified coloring material, and a process for producing the same. The first invention further includes a coloring material wherein the above solidified coloring material has been redispsersed in a solvent, and a process for producing the same. The first invention further includes a coloring material comprising an adduct formed by interaction between a soluble pigment precursor convertible to the insoluble pigment and a stabilizing agent comprising an organic compound having a structure or a functional group capable of stabilizing the dispersibility of the insolubilized pigment in the solvent. In particular, the coloring material according to the present invention can solve the above problems, and can be used in high concentration to easily form a pigment-dispersed polymer layer having excellent coating smoothness. This makes it possible to apply the coloring material to color filters having improved spectral characteristics (higher color purity, higher transmittance, and higher contrast) as compared with color filters using conventional coloring materials.
According to the second invention, there is provided a color filter using a coloring material comprising an insolubilized pigment dispersed stably in a solvent, said coloring material being produced by, in dissolving (1) a soluble pigment precursor, which is convertible into an insoluble pigment, in (2) a solvent capable of dissolving the soluble pigment precursor therein, allowing (3) a stabilizing agent, comprising an organic compound having a structure or a functional group capable of stabilizing dispersibility of the insolubilized pigment in the solvent, to further exist, and, in this system, converting said soluble pigment precursor into an insoluble pigment.
The coloring material may be in the form of a solidified coloring material produced by concentrating the above coloring material, or may be in the form of a dispersion produced by redispersing the resultant solidified coloring material in a solvent. The second invention further includes a technique wherein the coloring material is an adduct formed by interaction between a soluble pigment precursor convertible to the insoluble pigment and a stabilizing agent comprising an organic compound having a structure or a functional group capable of stabilizing dispersibility of the insolubilized pigment in the solvent. In particular, the coloring material according to the present invention can solve the above problems, and can be used in high concentration to easily form a pigment-dispersed polymer layer having excellent coating smoothness. This makes it possible to produce color filters having improved spectral characteristics (higher color purity, higher transmittance, and higher contrast) as compared with conventional color filters.
The third invention includes a color filter comprising a colored layer as colored pixels provided on a transparent substrate, the colored layer containing a specific pyrrolo[3,4-c]pyrrole derivative.
In the color filter according to this aspect of the present invention, a specific pyrrolo[3,4-c]pyrrole compound described later is contained as a pigment in at least one colored pixel. The particle diameter of the pigment is not more than the wavelength of incident light, that is, in the range of 1 nm to 300 nm in terms of average particle diameter, and, at the same time, the particle diameter distribution of the pigment falls within a specific range, that is, is within xc2x130% of the average particle diameter. By virtue of this, a lowering in transmittance caused by light scattering can be suppressed, and, in its turn, a much improvement in transparency of the formed colored pixels can be attained over the transparency of colored pixels obtained using conventional pigment-dispersed systems.
Further, the pigment produced from the coloring material has excellent display quality, and thus can easily form colored pixels which have ideal spectral characteristics as a color filter, specifically have a spectral characteristic curve in a visible region such that the light transmittance in a light absorption region is in the range of 0 to 20% while the light transmittance in a light transmission region is not less than 50%.
The amount of the pigment produced from the coloring material can be regulated by regulating the solid content of the matrix, specifically can be regulated in the range of 10 to 90% by weight, and can be easily used in higher concentration. Therefore, the contrast can also be significantly improved over the contrast attained in the conventional pigment-dispersed system, and can be set, for example, at not less than 2,000.
In general, dyes have unsatisfactory resistance to light, heat, solvents, and chemicals. On the other hand, pigments involve problems of a lack of dispersion, dispersion stability, transparency, profile sharpness of absorption spectra or transmission spectra, or diffusion. In this respect, Japanese Patent Laid-Open No. 188234/1995 proposes a pigment precursor which has a carbamate group and can be converted into a corresponding diketopyrrolopyrrole pigment having a size of nanometers by chemical, thermal, or photolytic means or by laser or other beam irradiation.
When the coloring material disclosed in Japanese Patent Laid-Open No. 188234/1995 is used, the affinity of the pigment precursor particularly for aprotic solvents is imparted by suitably selecting substituents D and E in formula (I). In this case, in order to broaden the range of selection of the solvent and, at the same time, to stably and homogeneously disperse the pigment in high concentration, the substituent should be made bulky to such an extent that the half or more of the molecular weight of the whole chemical compound is accounted for by this substituent. The introduction of the bulky substituent into the pigment, however, is very difficult. Further, these introduced substituents are finally eliminated by a chemical, thermal, photolytic, or radiation induced method. Therefore, finally increasing the pigment concentration becomes very difficult.
These adverse effects are particularly significant when the pigment precursor is converted to a pigment in a polymer layer. This makes it difficult to apply the pigment to the field of applications where good dimensional accuracy, particularly good coating smoothness, is required, such as color filters.
The present invention has been made under these circumstances, and can overcome the above problems, although the principle on which the problems can be overcome has not been fully elucidated. Specifically, according to the present invention, chemically cleaving a bond between N and Cxe2x95x90O in at least one pyrrolo[3,4-c]pyrroleketopyrrole group of formula (I) can enhance the affinity of the compound per se for various solvents, and thus enables a pigment-dispersed polymer layer having a high pigment content and excellent coating smoothness to be easily formed. This can realize a color filter having significantly improved spectral characteristics (higher color purity, higher transmittance, and higher contrast) over the conventional color filters.